Conduit coupling



Aug. I2.6, 1947. v R1 L.`AC:RES l l 2,426,332

` coHDUT coUPLING Filed Feb. 19, 1944 INVENTOR.

t BY

Patented Aug. 26, 1947 2,426,332 CONDUIT COUPLING 1:itichard L. Acres, Houston, Tex., assigner to William F. Curlee, Houston, Tex.

Application February 19, 1944, Serial No. 523,013

3 Claims (Cl. 285-146) This application relates in general to couplings or connectors for spirally wound iiexible conduits. Such conduits may be formed of a strip of metal or other suitable material and are provided with inwardly and outwardly turned edges so that when spirally wound these edges will interlock and provide a lost motion edge-to-edge connection for the convolutions of the strip forming the conduit, thereby forming a iiexible continuous conduit.

Various types of connectors have heretofore been provided for attachment to the end of spirally wound conduits such as just referred to so that the ends of such conduits might be secured to various ttings such as outlet boxes, switch boxes and the like. In the past however, such connectors or couplings have been of such a nature that they either distorted the conduit in such a manner as to cause adjacent convolutions of the conduit to become disengaged and the conduit thus opened exposing the electric wires or other parts contained therein, or they have been somewhat complicated in their structure and expensive to manufacture.

the interior diameter of various conduits which.

are nominally of the same diameter.

It is an object of this invention to provide a coupling for a flexible conduit oi the spirally wound type, which coupling will be very simple and relatively inexpensive to manufacture but which will lock itself rmly within the end of a flexible spirally wound conduit without the necessity for any tools for putting it in place.

Another object of this invention is to provide such a coupling which will adapt itself to various conduits of the same nominal diameter but of diierent pitches in their respective spiral windmgs.

Another object of this invention is to provide such a structure which may be employed in conduits of various actual internal diameters within reasonable limits so that it may be used inter-` changeably for conduits having the same nominal diameters but different actual internal diameters.

Other objects and advantages of this invention will become apparent from the following descrip tion taken in connection with the accompanying `drawing wherein are illustrated by way of example two embodiments of the invention.

in the drawing:` Y

Fig. l' is a side elevation of a coupling constructedin accordance with this invention.

Fig. 2 is an end elevation of the same coupling.

Fig. 3 is a View on an enlarged scale showing the coupling illustrated in Figs. 1 and 2, with this coupling partially inserted within the end of a flexible conduit, portions of the conduit being broken away and shown in section for thepurpose of illustration.

Fig. 4 is a view similar to Fig. 3 but showing the coupling after .it has been fully engaged within the exible conduit.

Fig. 5 is a view similar to Fig. a slight modiiication.

Fig. 6` is a view similar to Fig. 2 but showing the modication illustrated in Fig. `5.

Referring now more in detail to the drawing 1 but showing 'the coupling is illustrated as having a threaded end i with aradially extending flange 2 at the inner endV thereof, the threads l being adapted to receive a nut or the like for the purpose of clamping the coupling within an opening in an l outlet box or a switch box. l

Extending from the opposite side of the flange Z is a tapered shank portion 3 of somewhat re-` duced diameter having a projection i thereon consisting of a fractional convolution of a thread.

The coupling just described is adapted to be received into thev end of a flexible spirally Wound conduit such as illustrated in Figs. 3 and 4. Such conduits are formed by a spiral winding of a metallic or other strip or ribbon 5, such strip having one portion with an outwardly turned edge 6 and its opposite portion with an inwardly turned. edge l adapted to fit over and interlock with the cutwardlyturned edge E of the next convolution. it will be seen that a conduit formed vin this manner will have a spiral groove not only on its exteriorasurface but also on its interior surfaceas illustrated at 8.

As hereinbefore stated, usehas previously been made of the spiral groove 3 for the purpose of receiving a thread on a tubular part carried by a coupling so that the coupling might be screwed into the end of the conduit. In those instances,

however,` the tubular part upon which the thread` v.was formed was of such anature that it tted easily within the conduit and certain otherv provision was made for locking the conduit in place and preventing the coupling from being backed out. Thus, in some instances the end of the conduit was jammed up against a part corresponding to the flange 2 on the coupling so as to bulge the end portion of the conduit both inwardly and outwardly in an effort to lock it against the separation from the coupling. In other cases clamps were provided for thispurpose. It will `be appreciated also .that with the .use of a thread .compris-V ing more than one convolution, it was essential that the thread be of the saine pitch as the windy ings of the conduit, so that the coupling couldV not be used with a conduit having a different pitch from that for which the couplingwasmade.

In an effort to obviate the disadvantages of the, prior art and produce a more economical and more eicient structure I have found that it is'- possible to use a coupling in which the portion received into the spirallyrwound conduit has a projection whichmay or may noitconsist of aportion fof a rthread butA which'. does V'not extend `more than one4 complete con'volutionof .the spiral, and that with such a'tting itj'is possible' tov employ conduits of pitch windings which vary considerably from one another.' When onlya fraction of a convolutionis employedas illustrated inFigs. 1 to 4 inclusive, thereA is, ofcourse, engagement with thegroove 8 on' only one side of the conduit and conseduentlythe pitchof the groove has' little eiect on the engagement between this projection 4 and the groove 8.

I have found also that it is possible to provide sucha structure whichwill uponfullengagement with a spirally wound'flexible conduit offthe'na-A ture referred to lock itself Within such, conduit in suchl a 'manner that it cannot'berernoved without special tool's. To thisen'dI have discovered that it is necessary that, 'the smaller 'or `extreme end of the reduced tubular portiony 3 be Vmade of such an external diameter a'th'atvjit will. readily enter the end of the ilexible conduit, but this part should beso tapered that its diameter bjat 'its innerv end next to' the 'flange 2will be slightlyv greaterthan theinternal ydiar'neterrof the flexible conduit, this internal diameter-"being indicated in Fig. .3,by the letter, c'. In other words', the diameter a will'be slightly less than the diam-l eter c and the diameter b will be slightly greater than the diameter c. The 'diameter' a may 'be made small enough so that it will' t freely'within the smallest of theflexible conduits of one nominal si'zeand the diameter b may' be ma'd'e of such a. dam'etertnat it will be sughuy greater' than the'largest diameter C ofthe various conduits of the same nominal size. 'In'any event,` h'o'wev'er;

the angle d gnomo not be greater than-the critical angle for the materials 'employed in the'coupling and conduit 'respectively and it has been found in actual practice that with the customary steel conduit and with a coupling made of, die cast material customarily used forsuch purposes, an Vangle of substantially half ofthe critical ang'le is proper for 'the entire included angle between the' two opposite side surfaces 'of theportion 3.' That is, the' angle d would be approximately onefourth of the critical 'anglejndin the case o'f tnmaterms'referred to this would b'e'appfoinmately '3` 'toj 5, and the included' angle "df the 7o 10b. -Y .i Y 'Vg y., Y .e Another point to be observed isthat the dimensignj'zg, snouldjntbe la 'e enough tifa stretch the conduit radially suicntlytfor t'helasj;A cdnvoluf 4 tion on that end of the conduit on which the ribbon or strip terminates on the outside.

With the foregoing in mind i1; will be appreciated that when the coupling is fully engaged within the conduit as illustrated in Fig. 4, the end portion of the conduit designated by the numeral 9 will be slightly expanded and there will be a strong frictional engagement between the last convolution or so of the conduit and the surface of thejtapered tubular portion?, of the coupling.

Now it is to be noted that in inserting the coupling into the conduit it will be rotated in such a direction as will tend to unwind or loosen or expand the convolutions of the conduit. After it,ha.`s been fully engaged and the end portion of the conduit expanded and caused to frictionally grip` the inner end portion of the tubular part 3 onvthe coupling, then any effort to rotate the coupling in the reverse direction to disengage it from the conduit will tend to wrap the last convolution'fofy 'the' 'conduit more tightly upon this portion'and'it,will'be found that the coupling is'rmly locked in'position'withinthe conduit'.

Referring' now t'o` Figs'. 5 and 6, these figures are includedinbrder'to'illustrate a coupling having' substantially' one` complete 'convolution oi a thre'ad'fonthetapercd portion 3. This is indicated'at l0, 'and'it has been' found possible due tothe elastic nature' 0f' conduits formed in the manner above described and due to the'width of the'slct's 8in 'suchgconduits to employ a coupling having Ja, thread 'with 'one full convolutionY but not; substantially'greater 'than one full convolun tion, "to employ vsuch lcoinlingin conduits Vof pitches'varyingsubstantially' from each other.' 4It connectionjw th conduits of' diierent pitches, In

this 'connection vit'jis 'toloe noted'that' Fig. 6 clear- 1y sndwsthatthe'extreme ends of the thread section l@ are' more thanl'360 from' each other 4around the tubular portion'S, but that'tlie full thread does notQextendin excess of 3659?." v

`rI'h'e coupling'abovedescribedmaybe easily and without'any special 'tools screwed into the endl offy a conduitY unt i1"t"lfiey ilang'e 2v ony theA coupling abutsthe'endofthe conduit; "Thereupon no further'l rotation'ican' take 'place becauseV of the engagement betweenvthe fractional or full convolutioldthreadjand'the groove '8 on the interior of th'ejcondu'it', talen 'with' the abutment of the end of,Lthejconduitagainst the' coupling flange 25 However; the coupling cannot be backed out' of the conduit becauseof the frictional engagement betweenthe last'convolution of the conduit and the'surface'of the tubular portion 3 at the larger lA conduit coupling has thus been provided which iseXtremely simple tdnianuiacture, in which no exact Ytolerai'fices have to be maintained, and whichY will perform its function efliciently andA may be used without the necessity ior` any tools to'be employed. Havingy described my invention, what I claim 1S:

1. A coupling for a flexible conduit comprising a spirally Wound. Deed; Saidcouplin'e Comprising a tapered tubular'body having an Vexternal projection adjacent thesmall 'end thereof, said pro jection adapted to,`en ga'ge the spiral of said conduitj and draw said bodyy in to said conduit when said body is inserted into said conduit and turned in a direction tending to expand said spiral, and a part adapted to frictionally engage within said conduit to prevent rotation of said body the body part having the external projection thereon being4 of less diameter than the body part frictionally 5 projection in the form of a thread extending only 10 part Way around the tabular body adapted to engage the spiral of said conduit and draw said body into said conduit when said body is inserted into said conduit and turned in a direction tending to expand said spiral, and a part adapted to frictionally engage within said conduit to prevent reverse rotation of said body.

3. A coupling adaptable for use in conjunction with a flexible conduit made up of at least one spirally wound band to form an internal spiral groove, said coupling comprising a tubular body one end of which is of a size that it is easily insertable into such a conduit, a projection on said body adjacent said end, said projection extending only a part of the Way about the body, and adapted to t within a spiral groove Within such a conduit.

RICHARD L. ACRES.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 848,819 Freeman Apr. 2, 1907 1,842,216 Thomas Jan. 19, 1932 

